How to find information?

There are five sources of information for a Linux system: (1) manual pages, (2) info pages, (3) HOWTOs and documentation for programs, (4) help from programs and (5) the Internet Google search engine. Please bookmark this section and come back to it as needed. Just browse through it the first time quickly to see what options you have.

• Man pages: On-line manual pages are available on every Linux system. These are often the best sources of reference information about various programs on the system. Here are some useful pointers about man pages.
  • You want to know more about a certain command or program. To find out about a command and a description of what it does, type man <command_name>. Sometimes there may be more than one command with the same name. For example sleep <secs> command sleeps for the specified number of seconds. There is another man page for the sleep system call that you can call from a C/C++ program. Typing in man -a sleep (where -a is a command line argument to the man command) will show you all the man pages for sleep. It will show the first man page. If that is not the one you want, then press q to quit that page and then it will show you the next one on the same command and so on. You can use PageUp and PageDown keys to browse a manual page.

  • You want a one line summary of what a command does. To obtain a one line summary about a command type man -f <command_name>.

  • You want to find a command that does something you want to do. Think of an appropriate keyword that best describes what you are looking for and then type man -k <keyword>, which displays one line summaries of the commands that reference that keyword. For example:

    [alice@onyx]: man -k sleep
    Tcl_Sleep            (3)  - delay execution for a given number of milliseconds
    Tcl_Sleep [Sleep]    (3)  - delay execution for a given number of milliseconds
    apmsleep             (1)  - go into suspend or standby mode and wake-up later
    nanosleep            (2)  - pause execution for a specified time
    sleep                (1)  - delay for a specified amount of time
    sleep                (3)  - Sleep for the specified number of seconds
    usleep               (1)  - sleep some number of microseconds
    usleep               (3)  - suspend execution for microsecond intervals
    

    The numbers in the second column show the Section number for the manual page. So now we see several commands/calls that are related to sleeping. Find out more by doing man 3 sleep or man 1 sleep, where the number is the section number.

  • Man pages are organized into sections. The following shows the different sections and what they logically contain.

    
    

    Section	The human readable name
    1	User commands that may be started by everyone.
    2	System calls, that is, functions provided by the kernel.
    3	Subroutines, that is, library functions.
    4	Devices, that is, special files in the /dev directory.
    5	File format descriptions, e.g. /etc/passwd.
    6	Games, self-explanatory.
    7	Miscellaneous, e.g. macro packages, conventions.
    8	System administration tools that only root user can execute.

    
    

    For example, if you want to find out more about the printf library call, you can simply look for it in Section 3 using the following command:

    man 3 printf

    Otherwise if you say man printf, you will get the first man page found, which happens to be in Section 1. This command describes a printf that you can use from the shell and is different from the printf used in a C program.

• HOWTOs and program documentation. Linux has hundreds of excellent HOWTO documents available that describe specific topics. Go to the website http://www.tldp.org/docs.htmlfor a searchable list of HOWTOs. On your local system, look in the directory /usr/share/doc. There are hundreds of subdirectories, one each for specific programs that have more detailed information about that program.

• Ask a program: Many programs will display a message describing how to use the program when supplied with the command line option --help. For example, try

  passwd --help

• Google it! One of the best and fastest sources of information is the Google search engine on the Internet. Point your browser to www.google.com. Get familiar with this search engine and you may save years in your life.

• KDE Help. Under the KDE GUI desktop, you can access all the man and info pages in an integrated fashion. Type Alt and F2 together. It will pop up a window. In that window type in man:ls to access the man page for the command ls. Try this: Alt and F2 to get a pop up window, then type man:passwd. In the lab, you can also try man:submit